Spectroscopy Flashcards
What are the 5 components of optical spectroscopy
- Stable source of Radiant energy
- Transparent container for sample
- A device that isolates specific region of spectrum
- Radiation detector
- Signals processor and readout
Draw the gerneral layout for an optical spectroscopic method based on ABSORPTION
Draw the gerneral layout for an optical spectroscopic method based on FLUORESCENCE
Draw the gerneral layout for an optical spectroscopic method based on EMISSION
What are optical spectroscopic methods based on (total of 6)
- Absorption
- Fluorencence
- Phosphorensence
- Scattering
- Emission
- Chemilumenescence
What is Spontaneous Emission?
When an atom spontaneously jumps into a state with lower energy via the emission of a photon
What is Stimulated Emission?
When an atomic electron goes to a lower state after interracting with an elecromagnetic wave of a certain frequency via the emission pf a photon with the same phase, frequency, wavelength. etc..
What is a photon?
a stream of discrete “particles” or “wave packets of energy”
The energy of a photon is proprotional to the _________ of the radiation.
frequency
What is the wave nature of a single frequency electromagnetic beam?
The electric field oscillates in a **plane perpendicular **to the magnetic field, in a plane-polarized wave.
What happens to the electric field if radiation is unpolorized?
a component of the electric field would be seen in **all planes. **
what is Planck’s constant (**h) **?
6.63 x 10-34 J•s
1 J = _____ ev (electron volts)
______ J = 6.24 x 1018ev
What is the equation for frequency?
frequency= speed of light/ wavelength
v = c/λ
What is the equation for **Energy? **
Energy = Planck’s constant • fequency
E=hv
What is the equation to find refractive index?
Refractive index = (velocity in vaccum) **/ **(velocity in medium)
ni= c/vi
What is dispersion?
The variation in refractive index of a substance with wavelength or frequency
(ie. when a wavelength changes, so does the refractive index.)
What are the two types of regions in dispersion plots?
normal and anomalous dispersion region
how does a normal dispersion region look on a dispersion plot?
there is a gradual increase in refactive index w/ increasing frequency (or decreasing wavelength)
how does a anomalous dispersion region look on a dispersion plot?
there are sharp changes in the refractive index on the dispersion plot
what is **black body radiation? **
The continous emission spectrum of a substance when heated to incandescence.
Define **Relaxation. **
when an atom or molecule goes from excited state energy level to a lower energy level
What is Stoke’s Shift?
the negative difference in frequencies of emitted radiation from the incident beam.
The lowest state of a molecule is reffered to as _________.
ground state
What is spectroscopy?
the study of the interraction of various types of radiation with matter.
concerning waves, what is a period?
The time in seconds required for a particle a medium to make one complete vibrational cycle.
concerning waves, what is frequency?
The number of **vibrational cycles **per second
what is wavelength?
the distance between to maximas
what is the velocity of a wave dependent on?
The medium it’s passing through
Frequency is the inverse of _______
Period is the inverse of ______
what is a vaccum?
the absence of a medium
True or False?
excess energy can be released by heat.
TRUE
What is the name of this diagram?
Jablanski Diagram
what is the result of a jablanski diagram?
A SPECTRUM
what is the quantum theory?
atoms/moleules/ ions have limited number of discrete energy levels
Total Energy is the sum of __________
Eelectronic + Evibrational + Erotational
What is non-raidative relaxation?
loss of energy in small steps
Which relaxes faster, Fluorescence or Phosphorescence?
Fluorescence.
How does Stokes shift occur?
When a certain energy is put in a sample, you should get less energy out therefore the wavelength should be longer
How does Anti-Stokes shift occur?
When you put in a certain amount of energy in a sample, and end up getting MORE energy out. therefore having a shorter wavelength.
This can occur when heat is added
What are the four major categories of spectrochemical methods.
- Emission
- Luminescence
- Scattering
- Absorption
*all require radiant power, P *
Equation of Transmittance?
**T = (P/P0) x 100% **
What is the equation for Absorbance?
A = -log10T
A = log(P0/P)
A = 2 - log10%T
A= εbc
What is Beer’s Law?
Absorbance = [molar absorbitivity L •mol-1 •cm-1] [path length cm] [concentration of analyte]
A= εbc
Beer’s law is _________ for mixtures at a given wavelength
**Additive **
What are the limitations to Beer’s Law
- Only for dilute solutions
- Monochromatic radiation
- Path length must be the same
**high concentrated analyte makes it hard for absorption of radiation to happen**
Draw the general layout for a single beam instrument
Draw the general layout for a double beam-in-space instrument
Draw the genral layout for a double-beam-in-time instrument
what is a charged coupled device (CCD)
is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated.
integrated circuit etched onto a silicon surface forming light sensitive elements called pixels. Photons incident on this surface generate charge that can be read by electronics and turned into a digital copy of the light patterns falling on the device. like cellphone cameras
What is a Charge injection Device (CID)
A charge-transfer device used as an image sensor in which the image points are accessed by reference to their horizontal andvertical coordinates
Draw a general diagram of a photodiode array
What are the two types of wavelength selectors
- Filters
- Monochromators
What type of filters are there? Order from least best to best.
- Absorption Filters (inefficent)
- Interference filters (very effeicent)
- Holograohic Notch Filter (best)
what does a monochromator consist of.
- Entrance Slit
- Collimating lens OR Mirror
- Prism OR Grating to dispense radiation
- Focusing element
- Exit Slit
what does a **Photomultiplier Tube (PMT) **do?
Amplifies signals which allows for sensitive detection.
Photomultiplier tube is based on the ___________ ______ by _________ .
Photoelectric effect; Einstein
Define electron cascade.
propagation of electrons, build up of electrons.
What would be most likely used as optical source for wavelength of 200-400 nm
and what type of Electromagnetic radiation is in that region?
- H2 or D2Lamp (moest likely deterium lamp)
- UV
What would be most likely used as optical source for wavelength of 400-700 nm
and what type of Electromagnetic radiation is in that region?
- a Tungsten Lamp
- Visible light
what does laser stand for?
Light Amplification by stimulated emission of radiation
What are the four important prcoesses in laser action
- Pumping
- Spontaneous emission
- Stimulated Emission
- Absorption
what is pumping
excitation by electrircal, radiant, or chemical energy
What must happen in order for light amplification to occur?
the number of photons produced by stimulated emisssion must **exceed **the number lost by absorption. known as popultion inversion
(Ie. THERE IS MORE ENERGY IN THE EXCITED STATE THAN IN THE LOWER ENERGY STATES)
Population inversions are created by _______.
Pumping
Define what happens to produce a Three-Level Laser system
The transition for a laser radiation is between an excited state and the ground state
Define what happens to produce a Four-Level Laser system
there is an additonal excited state between the most excited state and ground state
What is the advantage of a four level laser system?
population inversions are achieved more easily, which is essential laser action
Repilca gratings are manufactured from a _______ _ ._
master grating
what is the equation for constructive interference?
diffrection order•wavelength =distance betweenn reflective sufaces( sin Ө1+ sin Ө2)
nλ = d(sin i + sin r)
What is the effective bandwidth of a filter
one half the bandwidth when the two slit widths are identical
what does a PMT consist of?
- photocathode
- Dynodes
- Anode
- Amplified Current
**in a vaccum tube**
Draw the basic structure of a PMT
What does a photocathode do?
Converts light (photons) into an electron current
What does a dynode do?
dynodes serve as an electron multiplier
what does an anode do?
delivers an output signal
1 Å = _____cm
_____Å = 10-8cm
1 m = _____nm
____m = 109 nm
10 Å = ____ nm
_____Å = 1 nm
1 MHz = ______Hz
______MHz = 106Hz
1 mol = ______photons
____ mol = 6.02 x1023 photons
1 m = ______ µm
_____ m = 106 µm
what is coherent radiation?
the phases of two waves that represent radiation differ by a known constant.
what is the work function of a substance?
the energy required to remove an electron from the surface of a substance
Define Photoelectric effect.
The energy contained inn a wave and particles depends on the frequency and intensity
what is the equation used to find refractive index when given angles
refractive index = (angle of incidence of “x”) / (angle of refraction of “x”)
nx= sin Өix**/ **sin Өrx
Equation to calculate concentrations in two unknown solutions
A1= (εm1•b•cm) + (εn1•b•cn)
A2= (εm2•b•cm) + (εn2•b•cn)
Equation to calculate the new concentration of a sample
Cx = (A1•Cs•Vs) **÷ **(A2- A1)Vx
why are holographic notch filters the best?
they provide a much narrower bandwidth and higher intensities
absorption flters are mainly used for what region?
visible regions
what is a disadvantage of using abosption filters?
they often block a significant portion of desired radiation
what is the range on a spectrum where visible light seen? (in nm)
400-700nm
Which source of energy is good for wavelengths from 160-380 nm
H2and D2Lamp
Which source of energy is good for wavelengths from 320-2400 nm?
tungsten lamp
Which source of energy is good for wavelengths from 200-1000nm
Xe arc Lamp
Which source of energy is good for wavelengths from 0.4-20 µm ?
nernst glower
Which source of energy is good for a line source of UV/Visible?
hollow cathode lamp
Which source of energy is good for a line source of UV/Visible/IR?
Lasers
__________ grating consists of ~300 blazes/min
Echelle
__________grating consists of ~1300 blazes/min
echellete
What are the units for reciprocal linear dispersion?
nm/mm
OR
Å/mm
